Technical Field
The present invention relates to gas turbine engine fan blade containment and, more specifically, to fan blade containment using ceramic tiles.
Background Information
Aircraft gas turbine engines include fan blade containment systems for retaining fan blades or fan blade fragments which may break off during engine operation. Fan blade failure can occur for a variety of reasons, but is commonly caused when a bird, hailstone, or any other foreign object strikes the engine fan while the engine is in operation. An uncontained fan blade failure may cause serious damage to the aircraft fuselage because of the high velocity of the fan blade or blade fragments. It is therefore necessary to provide some containment system near the engine fan for retaining any blade or blade fragments which break off the engine fan during operation. Such a containment system should be provided near the point where fan blade failure will cause the blade or blade fragment to travel.
Fan blade containment systems have been previously proposed for use in turbofan engines. These containment systems are designed to provide adequate retention of fan blade fragments without increasing the overall weight of the engine shroud. Certain prior containment systems utilized a metallic honeycomb structure for retaining fan blade fragments. Other systems disclose the use of ceramics as a part of an overall fan blade retention system, such as, in U.S. Pat. Nos. 4,289,447; 4,547,122; 4,646,810; and 4,818,176.
U.S. Pat. No. 5,447,411, issued to Curley et al. Sep. 5, 1995, and entitled “Light Weight Fan Blade Containment System” discloses a hard faced fan blade containment system for turbofan aircraft engines. The product combines a hard facing material, a high-strength fiber, and an elastomeric binder to form a fan blade containment system which is lightweight and effectively retains fan blade fragments. A hard material, such as ceramic or metal, is encapsulated in an elastomer and bonded to the impact face of the containment system to blunt sharp edges of failed blade fragments and to absorb some of the impact energy of the blade fragments.
Ceramic tiles offer additional energy absorption for a fan blade containment within a fan casing. However, the attachment of the ceramic tiles can be challenging because thermal expansion mismatch and high modulus will cause disbonds between the ceramic and containment structure. A rubber or elastomeric layer (typically RTV or sealant materials such as polysulfide) between the ceramic and structure can abate a Coefficient of Thermal Expansion (CTE) mismatch between the ceramic tiles and structure supporting the ceramic tiles. However, the RTV produces inconsistent bondline and gaps between the ceramic tiles which can allow the fan blade or blade fragments to penetrate and become the weak link during blade out. RTV also requires several hours to a few days to cure before subsequent process steps can be continued leading to long cycle times. The RTV and sealants are also not typically compatible with subsequent high temperature cure cycles.
It is highly desirable to have a fan containment system with ceramic tiles that has consistent and thin bondline and no gaps between the ceramic tiles. It is also desirable to have a fan containment system which abates a Coefficient of Thermal Expansion (CTE) mismatch between the ceramic tiles and structure supporting the ceramic tiles. It is also desirable to have a fan containment system with ceramic tiles that has short bond times and is compatible with subsequent high temperature cure cycles.